JP4006019B2 - Chlorine dioxide production method - Google Patents

Abstract

The invention concerns a process and an apparatus for continuously producing chlorine dioxide, the process comprising the steps of: feeding chlorate ions, acid and hydrogen peroxide as aqueous solutions to a reactor; reducing chlorate ions in the reactor to chlorine dioxide, thereby forming a product stream in the reactor containing chlorine dioxide; feeding motive water (5) to an eductor comprising a nozzle (26); bringing the motive water to flow through the nozzle and causing it to flow further through the eductor in an at least partially spiral or helical manner; transferring the product stream from the reactor to the eductor and mixing it with the motive water and thereby forming a diluted aqueous solution containing chlorine dioxide, and; withdrawing the diluted aqueous solution containing chlorine dioxide from the eductor.

Description

  The present invention relates to a method for producing chlorine dioxide from chlorate ions, acid and hydrogen peroxide.

  Chlorine dioxide is used in a variety of applications, such as pulp bleaching, fat bleaching, water purification and removal of organic materials from industrial waste. Since chlorine dioxide is not storage stable, it needs to be produced in situ.

  Chlorine dioxide is usually produced by reacting an alkali metal chlorate or chloric acid with a reducing agent in an aqueous reaction medium. Chlorine dioxide may be removed from the reaction medium as a gas, as in the methods described in US Pat. Nos. 5,091,166, 5,091,167 and EP Pat. No. 6,126,686. Normally, chlorine dioxide gas is then absorbed into water to produce its aqueous solution.

  For the production of chlorine dioxide for small scale units, eg water purification applications or small bleach plants, chlorine dioxide gas is not separated from the reaction medium, but the chlorine dioxide-containing solution is recovered directly from the reactor, if necessary after dilution with water It is advantageous to do so. Such methods are described in U.S. Pat. Nos. 2,833,624, 4,534,952, 5,895,638 and WO 00/76916, which are becoming commercially available in recent years. However, there is still a need for further improvements. In particular, it has proved difficult to obtain solutions containing sufficiently high concentrations of chlorine dioxide as required for certain applications such as recycled paper bleaching, bagasse bleaching, or small scale pulp bleaching. Also, high concentrations of chlorine dioxide can be beneficial in any application where it is important to minimize water flow.

  The object of the present invention is to provide a method which allows the direct production of chlorine dioxide in a highly concentrated aqueous solution.

  Another object of the present invention is to provide a method for the direct production of chlorine dioxide in aqueous solution with high production capacity.

  Yet another object of the present invention is to provide an apparatus for performing the method.

Surprisingly
Supplying chlorate ions, acid and hydrogen peroxide as an aqueous solution to the reactor;
Reducing chlorate ions to chlorine dioxide in the reactor, thereby producing a product stream containing chlorine dioxide in the reactor;
Supplying motive water to the eductor including the nozzle;
Allowing motive water to flow into the nozzle, which further flows at least partially, preferably substantially, into the eductor in a spiral or spiral manner;
Transferring the product stream from the reactor to an eductor, mixing it with motive water, thereby producing a diluted aqueous solution containing chlorine dioxide, and removing the diluted aqueous solution containing chlorine dioxide from the eductor. It was found that these objectives were satisfied by providing a continuous process for producing chlorine dioxide characterized by

Chloric acid ions can be supplied to the reactor as an aqueous solution containing chloric acid and / or metal chlorate, preferably alkali metal chlorate. The alkali metal may be, for example, sodium, potassium or a mixture thereof, among which sodium is most preferred. Unless chloric acid is used, another acid, preferably a mineral acid, such as sulfuric acid, hydrochloric acid or nitric acid needs to be fed to the reactor, of which sulfuric acid is most preferred. The molar ratio of H ₂ O ₂ to ClO ₃ ^— fed to the reactor is suitably about 0.2: 1 to about 2: 1, preferably about 0.5: 1 to about 1.5: 1, most Preferably from about 0.5: 1 to about 1: 1. Metal chlorates and chloric acids always contain some chloride as an impurity, but it is also possible to supply more chloride, for example metal chloride or hydrochloric acid, to the reactor. However, to minimize chlorine production, the amount of chloride ions fed to the reactor is low, suitably about 1 mol% or less, preferably about 0.1 mol% or less, more preferably about 0 mol%. It is preferred to keep the ClO ₃ ⁻ Cl ⁻ at 0.05 mol% or less, most preferably at about 0.02 mol% or less.

In a particularly preferred embodiment, an aqueous solution premixed with alkali metal chlorate and hydrogen peroxide, for example in the form of a composition as described in WO 00/76916, which is hereby incorporated by reference. Is fed to the reactor. Such compositions have from about 1 to about 6.5 mol / liter, preferably from about 3 to about 6 mol / liter of alkali metal chlorate, from about 1 to about 7 mol / liter, preferably from about 3 to about 5 It may be an aqueous solution containing at least one mole / liter of hydrogen peroxide and a protective colloid, a free radical scavenger or a complexing agent based on phosphonic acid, and the pH of the aqueous solution is preferably about 0.5. To about 4, preferably from about 1 to about 3.5, and most preferably from about 1.5 to about 3. Preferably, at least one phosphonic acid based complexing agent is present in an amount of about 0.1 to about 5 mmol / liter, most preferably about 0.5 to about 3 mmol / liter. When present, the concentration is preferably from about 0.001 to about 0.5 mole / liter, most preferably from about 0.02 to about 0.05 mole / liter. When a free radical scavenger is present, its concentration is preferably from about 0.01 to about 1 mole / liter, most preferably from about 0.02 to about 0.2 mole / liter. Particularly preferred compositions are 1-hydroxyethylidene-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), hexamethylenediaminetetra (methylenephosphonic). Acid), diethylenetriaminepenta (methylenephosphonic acid), diethylenetriaminehexa (methylenephosphonic acid), and 1-aminoalkane-1,1-diphosphonic acid, such as morpholinomethane diphosphonic acid, N, N-dimethylaminodimethyldiphosphonic acid A complexing agent based on at least one phosphonic acid selected from the group consisting of, aminomethyldiphosphonic acid, or salts thereof, preferably sodium salts. Useful protective colloids include tin compounds such as alkali metal stannates, particularly sodium stannate (Na ₂ (Sn (OH) ₆ ). Useful free radical scavengers include pyridine carboxylic acids such as 2, Preferably, the amount of chloride ions is about 50 millimoles / liter or less, preferably about 5 millimoles / liter or less, and most preferably about 0.5 millimoles / liter or less.

When sulfuric acid is used as the feed, it preferably has a concentration of about 70 to about 96% by weight, most preferably about 75 to about 85% by weight and preferably about 0 to about 80 ° C., most preferably about 20 It has a temperature of ~ 60 ° C. This is because it may be possible to operate the process substantially adiabatically. Preferably about 2 to about 6 kg of H ₂ SO ₄ , most preferably about 3 to about 5 kg of H ₂ SO ₄ are fed per kg of ClO ₂ produced. An equivalent amount of another mineral acid may also be used.

The net reaction leading to chlorine dioxide production can be described by the following equation:
2ClO ₃ ⁻ + 2H ⁺ + H ₂ O ₂ → 2ClO ₂ + 2H ₂ O + O ₂

  Its exact mechanism is complex, between chlorate and chloride to yield chlorine dioxide and chlorine (although always present in chlorate as a sufficient amount of impurities, even if not added separately) It is believed to involve an initial reaction followed by a reaction of chlorine with hydrogen peroxide back to chloride. However, in view of the net reaction, hydrogen peroxide is usually regarded as a reducing agent that reacts with chlorate ions.

  Reduction of chlorate ions to chlorine dioxide usually involves both liquid and foam, and production in the reactor containing chlorine dioxide, oxygen and in some cases some remaining unreacted feed chemical. Bring about the generation of logistics. Chlorine dioxide and oxygen can exist both as dissolved in the liquid and as bubbles. When metal chlorates and mineral acids are used as feed chemicals, the product stream will contain metal salts of mineral acids and usually also residual metal chlorates and mineral acids in addition to chlorine dioxide and oxygen. It has been found possible to obtain a conversion of chlorate ions to chlorine dioxide of about 75% to 100%, preferably about 80 to 100%, most preferably about 95 to 100%.

  It is preferred that the temperature in the reactor be maintained below the boiling point of the reactants and product stream at prevailing pressure, preferably from about 20 to about 80 ° C, and most preferably from about 30 to about 60 ° C. The pressure maintained in the reactor is suitably slightly below atmospheric pressure, preferably about 30 to about 100 kPa (absolute pressure), most preferably about 65 to about 95 kPa (absolute pressure).

  The reactor may comprise, for example, one or several containers arranged vertically, horizontally or inclined. The reactants may be fed directly to the reactor or via a separate mixing device. Suitably, the reactor is preferably a substantially tubular through-flow vessel or pipe and most preferably includes an apparatus for mixing the reactants in a substantially uniform manner. Such an apparatus may include a disk or the like with an aperture and disposed in the reactor, where metal chlorate and hydrogen peroxide are fed downstream of the disk, while acid is fed upstream of the disk. And flowed through the aperture and then mixed with the metal chlorate and hydrogen peroxide. Such an arrangement provides not only uniform mixing and stable operation of the process, but also a production rate with a high chemical efficiency maintained, especially in a reactor arranged substantially perpendicular to the upward main flow direction. It was found to give the ability to change. However, it is also possible to simply supply one type of reactant, for example an acid, to a supply line for another reactant or mixture of reactants, for example a mixture of metal chlorate and hydrogen peroxide.

  The length of the reactor used (in the main flow direction) is preferably from about 50 to about 800 mm, most preferably from about 350 to about 650 mm. It has been found advantageous to use a substantially tubular reactor having an inner diameter of about 25 to about 300 mm, preferably about 70 to about 200 mm. It is particularly advantageous to use a substantially tubular reactor having a preferred length to inner diameter ratio of about 12: 1 to about 1: 1, most preferably about 8: 1 to about 4: 1. A suitable average residence time in the reactor is in most cases from about 1 to about 1000 seconds, preferably from about 2 to about 40 seconds.

  The eductor, which contains any liquid, foam and gas, flows the product stream into the eductor and creates a suction force that mixes with the motive water to produce a diluted solution containing chlorine dioxide. The motive water is at least partly provided by any suitable device, such as twisted blades, internal slews, etc. (which may be integral or separated from the nozzle and located in or upstream thereof) In a spiral or spiral fashion. The nozzle may be of any suitable type and may include one or several holes.

  The eductor is preferably diluted in the direction of flow from the nozzle, into which a suction chamber (in which the product stream is transferred from the reactor) and a venturi section (through which in this case chlorine dioxide is contained). The aqueous solution is removed).

  The at least partially swirl or spiral flow of motive water increases the chlorine dioxide production capacity for a given motive water flow, thus separating conventional chlorine dioxide gas from the reaction medium and then absorbing it into the water ( It has been found that the present invention makes it possible to produce a product solution having a higher chlorine dioxide concentration than was possible only by a process that does not need to be carried out. Thus, it is possible to produce an aqueous solution containing about 1 to about 4 g / liter of chlorine dioxide, preferably about 1.5 to about 3.5 g / liter of chlorine dioxide.

  The process of the invention is particularly suitable for the production of chlorine dioxide on a small scale, for example about 0.1 to about 100 kg / hour, preferably about 0.1 to about 50 kg / hour in one reactor. For many applications, the preferred chlorine dioxide production rate is about 0.1 to about 25 kg / hour, most preferably about 0.5 to about 10 kg / hour in one reactor. A typical small-scale production unit usually contains only one reactor, but it is possible to arrange several reactors, for example up to about 15 or more, in parallel, for example like a bundle of tubes. .

  Furthermore, the invention relates to an apparatus for producing chlorine dioxide according to the above method. The apparatus includes a reactor with supply piping for chlorate ions, hydrogen peroxide and acid, the reactor further including a nozzle for motive water and motive water at least partially in an eductor in a spiral or spiral fashion. Connected to an eductor with a device for inflow.

  Preferred embodiments of the device are evident from the previous description of the method and the following description with reference to the drawings. However, the invention should not be limited to the embodiments shown in the drawings, but includes many other variations within the scope of the claims.

  Referring to FIG. 1, a vertical through-flow tubular reactor 3 is supplied with a premixed aqueous solution of sulfuric acid and sodium chlorate and hydrogen peroxide through a supply line 1 and through a line 2. In reactor 3, the feed streams are mixed and reacted to produce a liquid, foam and gas product stream containing chlorine dioxide, oxygen, sodium sulfate and some residual sulfuric acid and sodium chlorate. The eductor 6 is supplied with motive water through the supply pipe 5 and produces a slightly sub-atmospheric pressure that pushes the product stream from the reactor 3 through the pipe 4 to the eductor 6 where it is mixed with the motive water. To produce a diluted product aqueous solution. This diluted solution contains chlorine dioxide and other components from reactor 3 and is withdrawn as final product through line 8. Process control system including programmable logic controller (PLC), chlorine dioxide analyzer 9, pressure transmitter (PT) and flow transmitter (FT) supplies chemicals to reactor 3 and motivation water to eductor 6 The pump 10 is controlled.

  Referring to FIG. 2, a distribution disk 21 having an aperture is disposed at the lower part of the reactor 3, but is disposed above the inlet from the supply pipe 1 for sulfuric acid. The feed line 2 for the premixed sodium chlorate and hydrogen peroxide solution terminates in a distribution nozzle 20 located in the middle of the reactor cross section just above the distribution disk. A sodium chlorate and hydrogen peroxide solution is then sprayed across the cross section in the reactor 3, while sulfuric acid flows upward through the apertures in the distribution disk and on the distribution disk 21 with sodium chlorate and hydrogen peroxide. Mixed. After mixing, the reaction producing chlorine dioxide begins, producing a product stream of liquid, foam and gas, which stream is withdrawn through outlet 22 at the top of reactor 3.

  Referring to FIGS. 3 a and 3 b, the eductor 6 includes a suction chamber 25, a single hole nozzle 26 having an insert 27 (shown in FIG. 3 b as viewed through the nozzle) including a twisted vane 28, and a venturi portion 29. Motivational water is supplied from the supply pipe 5 through the nozzle 26 and the insert 27. The torsion blades 28 of the insert 27 allow water to flow further into the suction chamber 25 at least partially in a spiral or spiral fashion where it flows from the reactor 3 (see FIG. 1) through the pipe 4. A diluted chlorine dioxide containing solution is produced that is mixed with the stream and discharged from the eductor 6 through the venturi portion 29. The flow in the eductor produces a subatmospheric pressure sufficient to force the product stream to enter the eductor from the reactor.

The process equipment, including the reactor 3 and the eductor 6, is preferably made from a material resistant to hydrogen peroxide, sodium chlorate, sulfuric acid and chlorine dioxide. Examples of such materials include glass, tantalum, titanium, glass fiber reinforced plastic, PVDF (polyvinylidene fluoride), CPVC (chlorinated polyvinyl chloride), PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy polymer), Mention may be made of fluoroplastics such as ECTFE (ethylene chlorotrifluoroethylene) or FEP (fluorinated ethylene propylene), or the use of these materials as liner materials for structural materials such as steel or stainless steel. Suitable fluoroplastics are sold as trademark quinal (R), Teflon (R) or Haller (R).
The invention is further illustrated by the following examples.

  Chlorine dioxide was produced according to the present invention in the apparatus shown in the figure. In a vertical tubular reactor 3 having an inner diameter of 75 mm and a length of 610 mm, 40% by weight sodium chlorate and 10% by weight stabilized with a complexing agent based on 78% by weight sulfuric acid and phosphonic acid are added. An aqueous solution of hydrogen peroxide was continuously fed. Maintaining the reactor at a temperature of about 40-50 ° C. and an absolute pressure of about 84 kPa (about 17 kPa below atmospheric pressure) and supplying eductor 6 with motive water at an absolute pressure of 790 kPa produces a sub-atmospheric pressure. It was.

For comparison, chlorine dioxide was produced in the same manner, except that the eductor used did not include an insert into the nozzle that allowed the motive water to flow in at least partially in a spiral or spiral manner.
The results are shown in the table below.

本発明の方法はＣｌＯ₂生産速度及びエダクターから取り出された最終生成物溶液中のＣｌＯ₂濃度の両方の有意な増大を生じることが明らかである。

It is clear that the process of the present invention results in a significant increase in both the ClO ₂ production rate and the ClO ₂ concentration in the final product solution removed from the eductor.

1 shows a process schematic of the present invention. The reactor is illustrated. Figure 2 illustrates an apparatus for injecting eductor and motive water at least partially in a spiral or spiral fashion. Figure 2 illustrates an apparatus for injecting eductor and motive water at least partially in a spiral or spiral fashion.

Claims (18)

Supplying chlorate ions, acid and hydrogen peroxide as an aqueous solution to the reactor;
Reducing the chlorate ions to chlorine dioxide in the reactor, thereby producing a product stream containing chlorine dioxide in the reactor;
Supplying motive water to the eductor including the nozzle;
Allowing the motive water to flow into the nozzle, which further flows into the eductor at least partially in a spiral or spiral manner;
Transferring the product stream from a reactor to an eductor, mixing it with the motive water, thereby producing a diluted aqueous solution containing chlorine dioxide, and removing the diluted aqueous solution containing chlorine dioxide from the eductor A method for continuously producing chlorine dioxide, comprising:   The method of claim 1, wherein the motive water is further flowed into the eductor in a substantially spiral or spiral fashion.   The method according to claim 1, wherein the motive water is allowed to flow in at least partly in a spiral or spiral manner by twisting blades arranged in or upstream of the nozzle in the eductor.   3. A method according to any one of the preceding claims, wherein the motive water is introduced at least partially in a spiral or spiral manner by an internal swirl in or upstream of a nozzle in the eductor.   5. The eductor further comprising a suction chamber in which the product stream is transferred from the reactor in the direction of flow from the nozzle, and a venturi portion from which the diluted aqueous solution containing chlorine dioxide is removed. The method described.   The method according to claim 1, wherein the chlorate ion is supplied to the reactor as an aqueous solution containing a metal chlorate, and the acid is supplied to the reactor as a mineral acid.   The method of claim 6, wherein the mineral acid is sulfuric acid.   The process of claim 6 wherein the alkali metal chlorate and hydrogen peroxide are fed to the reactor in the form of a premixed aqueous solution.   The premixed aqueous solution is based on about 1 to about 6.5 mol / liter alkali metal chlorate, about 1 to about 7 mol / liter hydrogen peroxide, protective colloid, free radical scavenger or phosphonic acid 9. The method of claim 8, comprising at least one complexing agent having a pH of from about 0.5 to about 4. The amount of chloride ions fed to the reactor is ClO ₃ ^- in the Cl ^- is no more than about 1 mole%, any one process of claim 1 9.   11. A process according to any one of the preceding claims, wherein the product stream in the reactor comprising chlorine dioxide comprises liquid and foam.   The process according to any one of the preceding claims, wherein the temperature in the reactor is maintained from about 30 ° C to about 60 ° C.   13. A process according to any one of claims 1 to 12, wherein an absolute pressure of about 30 to about 100 kPa is maintained in the reactor.   14. A process according to any one of the preceding claims, wherein the reactor is a substantially tubular through flow vessel or pipe.   The method of claim 14, wherein the reactor is arranged substantially vertically.   The reactor includes an aperture and includes a disk or the like disposed in the reactor, and supplies metal chlorate and hydrogen peroxide downstream of the disk, while supplying acid upstream of the disk to the aperture. 16. A process as claimed in any one of claims 14 to 15, wherein it is introduced and then mixed with the metal chlorate and hydrogen peroxide.   The method of claim 15, wherein the main flow direction is upward.   18. The chlorine dioxide production apparatus according to claim 1, comprising a reactor equipped with supply pipes for chlorate ions, hydrogen peroxide and acid, wherein the reactor is a nozzle for motive water. And a manufacturing device connected to an eductor comprising a device for further flowing motive water at least partially into the eductor in a spiral or spiral manner.

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